1. Field of the Invention
The present invention relates to an optical disk having a projection for preventing full contact of the recording side of the disk upon engagement with a supporting surface.
2. Description of the Related Art
Recently, optical disks having various structures with enhanced features and dramatically increased storage capacities have been developed to improve, among other things, their recording density. The currently-used high density optical disks include DVD-R, DVD-RAM, and the like.
FIG. 1 and FIG. 2 illustrate diagrams of a high-density optical disk according to a related art and the dimensions of various elements. These figures show a disk 20 having a thickness of 1.2 mm and a diameter of 120 mm. A via hole 22 is formed at a central portion of the disk 20. The disk 20 has an outer recording layer 10 and a central portion 24 of the disk 20 having the via hole 22. A diameter of the via hole is about 15 mm, and a diameter of the central portion is about 44 mm. The recording layer 10 is formed at a location about 0.1 mm from a surface of the disk 20 on which light is incident.
In the illustrated disk, a protecting layer 30 is formed on the recording layer 10 to protect the recording layer 10. The protecting layer 30 is formed by attaching a transparent plastic film, such as a polycarbonate sheet, to the recording layer 10 or spin-coating a UV-hardening resin on the recording layer 10.
The process of spin-coating on the protecting layer 30 is explained as follows.
First, a UV-hardening resin in a liquid state is dropped on the recording layer 10 adjacent to the central portion 24 of the disk 20. The disk 20 is then rotated at a predetermined spin speed based, in part, on the viscosity of the resin. The spinning disk causes the UV-hardening resin to spread across the recording layer 10 from the central portion to the circumference in response to centrifugal force. Once the resin spreads across the surface of the recording layer 10, the UV-hardening resin coated on the disk is hardened by exposing the resin to UV rays.
However, spin-coating fails to evenly distribute the UV-hardening resin across the recording layer 10 in creating a protecting layer of a uniform thickness. Instead, as illustrated in FIG. 1, the thickness of the UV-hardening resin formed on the recording layer 10 becomes thicker as the protecting layer 10 approaches the outer circumference of the disk 20.
Hence, thickness deviations in the protecting layer 30 interfere with the recording/reading of information on/from the recording layer 10.